Mechanical thrombectomy devices such as stentrievers are frequently used to recanalize blocked cerebral arteries in patients suffering from acute ischemic stroke. The method of use of such a device involves introducing a guidewire endovascularly and advancing it through the vasculature until it is distal of the obstructive clot. A guide catheter is then passed over the guidewire to a location proximal of the clot. A microcatheter is passed over the guidewire through the guide catheter to a location distal of the clot. The guidewire is then withdrawn proximally to allow for the introduction of the clot retrieval device in the collapsed configuration through the microcatheter. A generic clot retrieval device is comprised of an elongate member and a clot engaging body connected to the distal end of the elongate member. The clot retrieval device is advanced distally within the microcatheter until is it situated within the clot. At this stage the microcatheter is withdrawn and the device will expand. In its expanded configuration the device exerts a radial force on the clot thus capturing the clot against the walls of the vessel. Once the clot has been captured by the engaging body of the device and aspirating has commenced, the device and the clot are withdrawn towards the guidecatheter. The device and the clot are withdrawn into the guidecatheter and removed from the vasculature.
The force required to retract the device may have undesired consequences. In order to dislodge the clot from the vessel a force must be applied to it through the stentriever device. This force is effectively applied to the vessel in which the clot is lodged and to the distal vascular bed, placing these vessels in tension and placing the vessels proximal of the clot in compression. Once the clot begins to move there is relative movement between the stentriever device and shaft and the vessel wall. This relative movement can cause abrasion and damage to the endothelia and underlying layers of the vessel wall, which may result in a dissection or perforation, or could give rise to the subsequent formation of thrombus which could then be liberated to create an additional stroke.
The force that must be applied to dislodge and retract the clot is dependent not only on how well lodged the clot is in the vessel, but also on the frictional losses that occur where the stentriever device contacts vessel walls or the inner surface of the catheter through which it passes. Thus it would be advantageous to have the use of a device which acts as a shield between the elongate shaft and the vessel wall. In the preferred embodiment the invention would remain in situ in the vessel as the elongate shaft is being retracted and absorb the tension which would normally be exerted on the shaft and the vessels. Preferably the invention would have a low friction inner surface and a higher friction outer surface. This would allow the shaft to move more fluidly within the device while the device remained in the vessel. The present invention includes these features and improves upon the methods of clot retrieval previously discussed.